In standard gas turbines, the higher turbine inlet temperature required for increased efficiency results in higher emission levels and increased material and life cycle costs. This problem is overcome with the sequential combustion cycle. The compressor delivers nearly double the pressure ratio of a conventional compressor. The compressed air is heated in a first combustion chamber (e.g. via an EV combustor). After the addition of a first part, e.g. about 60% of the fuel, the combustion gas partially expands through the first turbine stage. The remaining fuel is added in a second combustion chamber (e.g. via an SEV combustor), where the gas is again heated to the maximum turbine inlet temperature. Final expansion follows in the subsequent turbine stages.
In so-called SEV-burners, e.g. sequential environmentally friendly v-shaped burners, generally of the type as for instance described in U.S. Pat. No. 5,626,017, regions are found, where self-ignition of the fuel occurs and no external ignition source for flame propagation is required. Spontaneous ignition delay is defined as the time interval between the creation of a combustible mixture, achieved by injecting fuel into air at high temperatures, and the onset of a flame via auto-ignition. A reheat combustion system, such as the SEV-combustion chamber, also called SEV-combustor, can be designed to use the self-ignition effect. Combustor inlet temperatures of around 1000 degrees Celsius and higher are commonly selected.
For the injection of gaseous and liquid fuels into the mixing section of such a premixing burner, typically fuel lances are used, which extend into the mixing section of the burner and inject the fuel(s) into the oxidizing stream (22) of combustion air flowing around and past the fuel lance. One of the challenges here is the correct distribution of the fuel and obtaining the correct ratio of fuel and oxidizing medium.
SEV-burners are currently designed for operation on natural gas and oil. The fuel is injected radially from a fuel lance into the oxidizing stream and interacts with the vortex pairs created by vortex generators, as for instance described in U.S. Pat. No. 5,626,017, thereby resulting in adequate mixing prior to combustion in the combustion chamber downstream of the mixing section.